Multiplex radio system



April 6, 1926.

H. F. ELLIOTT ET AL.

MULTIPLE RADIO SYSTEM Filed Jan. 9, 1922 M w 3 E I N V E N TOR Harald f". f/liolf' James A. Mil/en a Li Lb WITNILZSS 1 Patented Apr. 6, 1926. V

HARO D F. ELLIOTT LJAI S ARTHUR MILLER, or PALO ALTO, CALIFORNIA, As-v S eNonS, BY MESNE ASSIGNMENTS, TO FEDERAL TELEGRAPH COMPANY, or SAN I 1,579,921 PATENT YoFFI rnANcIsoo, cALIronNIn, A CORPORATION OFCALIFORNIA.

MULTIPLE RADIO SYSTEM.

Application filed January 9, 1922. Serial No', 527,883. 3

T0 all'whom it mag concern: V

Be-it'known that we, HAROLD F; ELL OTT and J AMES ARTHUR MILLER, citizens of the United States, and residents of Palo Alto, in the county of'Santa Clara and State of California, have invented a new and useful Multiplex Radio System, of which the following is a specification. I I

This invention relates to a multiplex radio transmitting system, utilizing morethan one antenna. a 7 1 It is often desirable to operate a plurality of transmitters for radio signaling from the 1 "same building, so as to economize in space fzid in the number of employees.

I Since ch transmitter is assoclated with its own i antenna, the result is that a plurality offantennae are placed near each" other. This usually has the objectionable effect that there is 'moreor less capacitive or electrostatic coupling between them. Due to this coup-v ling, the two transmitter circuits are to some extent int-er-dependent.- Whilev in some types of transmitters,such a condition is not serious, it has been found. thatan ob ect1onable interference between theclrcults results when are converters are usedas the genera"- tors of radio frequency. Itis oneof the ebjects of our invention to render the operation 'of such transmitter circuitssubstantially independent. of each other, so that signals maybe sent from any one of them without danger of interference from any of the othersf Another objectof our i-nvention is to render it possible to start or stop any ofthe transmitters without influencing'the operation of the other transmitters. p

The invention possesses other advantageous features, some of which, with the fore going, will be set forth at length in the following description where we shall outline'in' full those forms of the invention which We have selected for illustration in the drawings accompanying and forming part of the present specification. Several embodiments of our invention are shown in the drawings, but it is to be understood that we do not limit ourselves to such forms, since the in vention as expressed in theclaims may be embodied in other formsas well. Referring to the drawings: P

Fig.1 isa wiring diagram of a system embodying one form of our invention; .and

Figs. 2 and 3 are wiring diagrams show- 111g further modlficatlons. I

In the following dlscussionsystems will be described each using only two transmitters operating at substantially difierent frequencies, but it is to be understood that the schemes elucidated are fully as applicable to systems using any number of transmitters.

One of the schemes by which'it is possible to" overcome the disturbing effects of one source uponanother is illustrated in Fig, 1.

To obtain this result, we arrange matters in such a waythat the antenna system of each transmitter has a relatively high impedance at the frequencies of the othertransmitters, and this relatively high impedance:is not substantially altered by the starting or stopping of the transmitters, or Whether signals are sent or not. 5

1 The establishment of a high impedance for interfering currents may be accomplished in the following manner :The arcs 35 and 3601' other sources of. high frequency our- 7 rent, are arranged to a feed the transmitting circuits 13- 14rl5 and 1819'2O respectively. In series with are 35are placed the inductor 37' and condenser 38; in series with are 36 are placed the inductor 39 and condenser 10. These elements are all in series in the antenna circuits. .The circuit consisting of are 35 inductor37 and condenser 38 is tuned to the frequency of transmission of theassociated antenna circuit; and the circuit consisting of are 36, inductor39 and condenser40 is similarlytuned to the frequency of trans mission of the associated antenna circuit. Paralleling each of these tuned circuits is a circuit consisting'for example of a resistor 41 or 42; This resistor, serves to by-pass and damp out harmonics or other objectionable current that would otherwise be present'in the circuits. Since eachantenna circuit is tunedto its ownfrequency, the impedance of either of themsuch as18'-19-20 is comparativelylarge for currents of frequencies differing substantially from its own. Thus currents induced in this antenna circuit by current flowing in the, antenna circuit 13- i k-15 are relatively low in value. The

. interfering currentthat can pass through the tuned circuit 40-39-36 is still lower,

since its impedance is also high for frequenciesother than it's'own. The voltage induced across this circuit is also low, and thus the operation of the twosources and 36 on adjacent antennae do not interfere with each other. The by-pass action of resistors 41 and 42 not only limits the operationof the sources to certain definite frequencies, but also permits the interfering currents from the adjacent antenna to be conducted to ground without passing through the source. Other forms of impedance may, of course, be substituted for theresistors. The operation of such by-pass circuits to limit the source to a definite frequency is described and claimed in an application in our names, filed concurrently herewith, entitled .Radio frequency system, Serial No. 527,884.

Somewhat similar principles of operation to those just described, .are utilized in the form ofour invention illustrated in Fig. 2. In this form, means are also provided for increasing the'eificiency of the source, which may be an" are or bulb, by controlling the point at which it operates on its currentvoltage characteristic. In the figure there are shown the two arcs or other sources 43 and 44, supplying. respectively the: antenna circuits 13144745 and 18194846. The antenna circuits are closely coupled by means of coils 47 and 48 to their respective sources. Thus are 43 supplies radio frequency current to a circuit consisting of the inductor 49, condenser 50, coils 51 and 52, and the coils 53' and 47 The coils 53 and 47 form an air cored auto transformer, the coil- 47 forming a portion of the secondary circuit'supplying the antenna. It is of course possible to substitute a: conventional transformer for the auto. transformer 4753. The arc circuit between point 54 and ground 55 is tuned to the frequency which it is desired to use, the inductor 49 and condenser 50 being in the circuit for the purpose of tuning. The resistor 56 or other form of impedance is connected across this tuned circuit. The operation of this system to increase the efficiency of the source and to confine its operation to a definite frequency is described and'claimed in another application in our names filed concurrently herewith, entitled Radio frequency system, Serial No. 527,885.

'In order to neutralize whatever coupling there may be unavoidably present between the inductor 49 and the transformer coils 53 and 47, the coils 51 and 52arecoupled to theproper extent. This is especially useful when uniwave signaling, is used, since if -the coupling is not neutralized, a small amount of energy may still be radiated although no signal is supposed to be sent. Uniwave signaling may be readily accom- V plished by short circuiting the resistor 56 to stop the sendin'gof waves. For this purpose relay keys 57 and 58 may be closed. To keep the load on the source constant, a secondary circuit may be coupled to the inductor 49, COHSlStlDg of the coil 59 and resistance 60.

.This circuit is open when waves are sent,

but may be closed simultaneously with the closing of keys 57 and 58, by ineans'of key 61. Itispossible'to regulate theamount of energy dissipated in circuit 59 60'61 either by properly choosing the value of resistance 60 or by varying the degree of 0011- 7 pling between the: coils 49 and 59. The resistor 56 in connection with the tuned local circuit and the'tuned antenna circuit effectively by-passes the interfering currents, as explained in connection with Fig. 1. The 50 source'is also confined to operation at the correct frequency without higher harmonics. Due tothe transformer action,the current in the intermediate or primary circuit is lower than would be the case without the use of the transformer action. The result is not only a reduction in the losses-in this circuit, but also in the size, weight and cost of suchapparatus as the inductor 49 and condenser 50in this circuit. Thus the use of this system renders practicable the operation of filter circuits with high power transmitters The elements shown in the system connected.

to the other antenna 18 are entirely similar to those described in connection with anten-. na 13.

In Fig. 3 is shown a simpler scheme for preventing interference between transmitting systems. Inthis case a resistor 64 and a stopping condenser 65 are shunted around the-source 62 and serve to by-pass the objectionable interfering currentsj The stopping condenser65- prevents current from the generator 16 from being wasted through the resistor 64. The other antenna 18 is suplied froma system including a source of high frequency oscillations 63, and other elements equivalent in every way with those just described. in connection with antenna 13.

We claim:

1. In a multiplex radio frequency'transmission system, a plurality of antenna circuits, eachadapted to be independently operated at frequencies that differ substantially, and each having an antenna that is placed near the others, sources for producing high frequency oscillations in each of the antenna circuits, and means for preventing substantial interference between the circuits, comprising a circuit for each source forming a by-pass, said circuit being connected between points liaving minimum potential difierence for the frequency of operation of the source with which it is associated.

2; In a multiplex radio frequency transmission system, a plurality of antenna transmitting circuits, each adapted to be independently operated at frequencies that differ substantially and each having an antenna that. is placed near the others, means for producing oscillations in each antenna circuit, and means for preventing substantial interference between the circuits, compris ing an energy consuming device for each transmitting circuit, and means for connecting said device in each circuit so that it may conduct the interfering current from the other transmitting circuit around the source of oscillations.

3. In a multiplex radio telegraphy system, a plurality of antenna circuits having sub stantially different frequencies and having antennae-near one another, sources for producing high frequency oscillations in each of the antenna circuits, and a by-pass circuit for each source, whereby substantially all currents produced by interference of any of the other sources is passed through these by-pass circuits.

4. In a multiplex radio telegraphy system, a plurality of antenna circuits having substantially different frequencies and having antennae near one another, sources for producing high frequency oscillations for each of the antenna circuits, a circuit connected in series between each antenna circuit and its source, the source and this s circuit being tuned to be resonant at the frequency of the source, and a circuit in each antenna system bridging this resonant circuit.

In testimony whereof, We have hereunto set our hands. HAROLD F. ELLIOTT.

JAMES ARTHUR MILLER. 

